High-Definition Multimedia Interface (HDMI) is a protocol for digital transmission of audio and video data from audiovisual sources to audiovisual destinations (also referred to as “sinks” in HDMI literature). Detailed specifications for HDMI can be obtained from the www.hdmi.org website. Recent HDMI specifications are HDMI 1.4 and HDMI 2.0, which are incorporated herein by reference. Similar protocols are defined by the DisplayPort standard from the Video Electronics Standards Association (VESA). Detailed specifications for DisplayPort protocols can be obtained from the www.vesa.org website.
FIG. 1 illustrates the main components of an HDMI link 100. These include the source 110 (e.g. a Blu-ray Disc player); the cable 120; and the sink 130 (e.g. a television). The HDMI standard uses Transition Minimized Differential Signaling (TMDS) to carry high-speed audiovisual data from the source to the sink. The cable in FIG. 1 may for instance be a conventional coax HDMI cable. The HDMI cable carries digitized audiovisual data via three differential TMDS channels 140: TMDS Data0, TMDS Data1, and TMDS Data2, commonly jointly abbreviated simply as TMDS Data. A fourth differential TMDS channel, 150, called TMDS Clock, carries a subrate version of the clock used to create the digital TMDS data signals. There are also a collection of low-speed lines which carry control and configuration signals. These lines are known as: “Hot Plug Detect” (HPD), “Display Data Channel” (DDC) which is composed of “Serial Data” (SDA) and “Serial Clock” (SCL), Consumer Electronic Control (CEC), “Utility”, and “+5V Power”. Along with other control information, these lines are used to negotiate video parameters (e.g. resolution, frame rate, and/or color depth), audio parameters, and perform the encryption key exchange for High-Bandwidth Digital Content Protection (HDCP). These functions in large part contribute to the prevalence of HDMI by allowing the highest quality video jointly supported by the source, HDMI link, and sink.
When characterizing video quality, the most commonly known parameter is the display resolution. Most high-end displays available today support “1080p” resolution (also known as “2K”) which is 1920×1080 pixels. However, new “4K” displays with four times as many pixels (i.e. a 3840×2160 display resolution) are introduced to the market. Some manufacturers have even exhibited “8K” displays supporting resolution (i.e. 7680×4320 pixels), another quadrupling of the resolution above “4K” displays. Commensurate with each quadrupling of the number of pixels is a dramatic improvement in picture sharpness but also a quadrupling of the video data rate (if all other factors are constant, such as color depth and frame rate as described next).
A less well known, but still highly important, set of parameters influencing video quality is the color depth, which describes the color space quantization. Parameters are:                i) “bits per pixel”, selected from {24, 30, 36, and 48}, which defines the number of bits representing the color of each pixel, and        ii) “chroma subsampling”, commonly selected from {4:2:0, 4:2:2, and 4:4:4}, which defines how the Cr (red complement) and Cb (blue complement) chroma components are sampled in the YCrCb chroma space with 4:2:0 being the coarsest subsampling and lowest color quality and 4:4:4 being the finest sampling and highest color quality.        
More bits per pixel and finer chroma subsampling result in richer, more vibrant color. Coarse color quantization and chroma subsampling are often evident by duller color and the presence of what is known as “color banding” where an abrupt change in color quantization levels can be seen in an image or scene with an intended smooth color gradation. Unfortunately, while deeper color brings higher quality video, it comes at the cost of higher bandwidth. FIG. 2 illustrates how deeper color (more bits per pixel and finer chroma subsampling) requires higher bandwidth capacity by the different colored curves in the graph for a 4K resolution display.
A third key parameter in video quality is the frame rate. Slower frame rates such as 30 frames-per-second (fps) below can produce visibly noticeable jitter, choppiness, or chatter in video involving fast motion as may be seen in an action scene, sporting event, or even the panning of a video camera. This choppiness is dramatically reduced at 60-fps and is generally noticeable only when deliberately focused on. At 120-fps, this jitter is not perceivable for the human eye. While reducing jitter to imperceptible levels is desirable, it unfortunately requires ostensibly more bandwidth. The required video bandwidth scales proportionally with the frame rate, so 120 and 60-fps video require 4 times and 2 times, respectively, the bandwidth of 30-fps video. This trend is also illustrated in FIG. 2. Furthermore, 3D systems require another doubling of video bandwidth in that full video information must be delivered for both left eye and right eye.
FIG. 2 illustrates examples 200 of video data rates in various video systems. As is evident from FIG. 2 and the preceding discussion, higher quality video requires higher video throughput. To appreciate the severity of the current bandwidth constraints of HDMI and how it is limiting video quality, consider the vertical axis of FIG. 2. A recent version of the HDMI specification (version 1.4) supports up to 3.4-Gb/s of throughput on each TMDS data line, for an aggregate throughput of 3*3.4-Gb/s or 10.2-Gb/s for the entire cable. That is enough bandwidth to carry a high-frame rate deep color “HD” video signal, e.g. 1080p resolution with 48-bit color and 4:4:4 chroma sampling at 120-fps which requires an aggregate bandwidth of 8.91-Gb/s. However, simply changing the resolution from 1080p to 4K, while keeping the deep color and 120-fps, would quadruple the required bandwidth to 35.64-Gb/s which greatly exceeds the 10.2-Gb/s capabilities defined in HDMI 1.4. In fact, HDMI 1.4 only allows for 4K resolution at a slow 24 or 30-fps. Furthermore, the color must also be compromised to reduce the bits per pixel or chroma sampling in order to fit within HDMI 1.4's bandwidth capabilities. The result is that even though displays today are capable of producing 4K (and even 8K in ultra-high-end demonstrations), there is no readily available system to communicate the larger data volume with deep color and high frame rates.
HDMI 2.0 offers up to 18-Gb/s and supports 2160p60, which is 4K at 60-fps. At this rate, it does not enable deep color, which would require the previously mentioned 35.64-Gb/s. It falls far short of offering 8K capabilities.
Thus, while today's HDMI based systems generally transmit the highest quality signal jointly supported by the source, HDMI link, and display, it is the rate limitations on the TMDS data in the HDMI protocol that is the system limitation.
Consequently, there is an unmet need for methods and systems for communicating data that support the higher data rates associated with the capabilities of more advanced displays and sources, such as displays with high resolution, deep color, and/or fast frame rates.